Raleigh Gran Prix BB Question
 

I am working on a Gran Prix from the early 70's for a friend. I would love to ditch the heavy, steel cottered crankset in favor of an alloy one (cotterless of course!). The bb shell is 70mm and I seem tpo remember that this denotes the proprietary Raleigh threading. Can anyone tell me what the easiest/least expensive path is to convert this crankset?

I believe Sheldon Brown says you can use a MTB spindle in the existing cups. Check his site.

a #5 spindle should get you there.

Are the threads Whitworth , at this age ? If so, I do not think that you can replace the bb cups with a Japanese set. Anyone know for sure, for my future reference ?

No need to replace the cups.

When you have the old crankset off and the new one not yet on, weigh them both. I'm curious exactly how much weight you'll save. When I compared the steel Williams crank on my Norman to a late 90's Shimano 105, I found the weight difference to be pretty negligible.

Replacing the cups is not an option; Raleigh used a proprietary 26 tpi thread while 24 tpi is standard. You can run a 24 tpi tap through there, but it will remove a lot more material than you want. Fortunately, as OFG said, there is no need to replace the cups.

^Cup replacement is an option but you'd have to buy expensive Phil cups to replace them. I just put a 5 spindle in my GP and it's working well.

Thanks all for the info. Where can you get a #5 spindle? If ebay, is there a specific search you would use like #5 spindle (duh) or something else?

Ask at you LBS. They probably have one in a drawer.

Last one cost me $3.

True that steel cranks themselves are not bad or excessively heavy, but the chainrings bend too easily and need truing. Also, the cotter pins are a *****. I remember Nervar made a steel cotterless crank. Nothing wrong with that.

I think that a "5" spindle is actually Japanese nomenclature. Sutherland's has some pretty good info on this, and Sheldon Brown's is not too shabby either. If you want the relevant pages from Sutherland's (which is downloadable here), I'll try to help.